MVR (mechanical vapor recompression) process device for sintering desulfurization and denitrification wastewater treatment

Abstract

The utility model belongs to the technical field of wastewater treatment, and relates to an MVR (Mechanical Vapor Recompression) process device for sintering desulfurization and denitrification wastewater treatment. The MVR process device comprises a wastewater pretreatment module and an MVR low-temperature forced circulation crystallization module which are connected in sequence; the sintering desulfurization and denitrification wastewater firstly enters the wastewater pretreatment module and then enters the MVR low-temperature forced circulation crystallization module, and the wastewater treated by the system can be directly recycled. Meanwhile, the process device disclosed by the utility model can be operated at low temperature; and therefore, scaling of a process device and corrosion of equipment can be avoided. The process device disclosed by the utility model is short in operation flow, small in occupied area and capable of fully utilizing the heat of secondary steam and greatly reducing the cost. In addition, the equipment is simple and convenient to maintain, long in chemical cleaning period, effective and stable in scaling control and long in service life, and is very potential wastewater treatment equipment.

Description

Technical Field

[0001] The present application belongs to the technical field of wastewater treatment and relates to an MVR process device for treating sintering desulfurization and denitrification wastewater. Background Art

[0002] The desulfurization and denitrification wastewater generated in the steel sintering desulfurization and denitrification process is generally treated with pretreatment (removal of suspended solids) + steam stripping deamination and other processes, and thallium removal processes are configured as needed. Because the desulfurization and denitrification wastewater contains Class I pollutants such as arsenic, lead, and thallium, this treatment process meets the Class I pollutant emission standards and then flows into other water treatment systems for further treatment or dilution of other pollutants such as COD and total nitrogen.

[0003] Wastewater treated by this process still has high salt, chloride, sulfate, and COD characteristics. Entering other water treatment systems will cause water quality fluctuations in these systems and affect their normal operation. Under the current requirements of water conservation, emission reduction, and salt reduction and control, the entry of such high-salt water into the wastewater reuse system has a significant impact on the water quality of the entire plant. In actual operation, the reuse water treatment process is mostly based on membrane methods. Although the volume of this high-salt wastewater is relatively small, it has a significant impact on the membrane method. Operational practice has shown that the reuse water treatment process is prone to scaling and membrane fouling, resulting in reduced treatment capacity, shortened membrane element life, and greatly affecting treatment stability. If this high-salt water is diluted with other treated water and discharged, the total amount of pollutants such as COD and total nitrogen may exceed the discharge standard.

[0004] In summary, the amount of high-salt wastewater generated in the steel sintering desulfurization and denitrification process is small, and it has the characteristics of high COD and high total nitrogen content. The existing technology lacks a treatment process device with high stability, high safety and low cost. Utility Model Content

[0005] In view of the current lack of an excellent treatment method for wastewater with high salt content generated in the steel sintering desulfurization and denitrification process, the purpose of this application is to provide an MVR process device for treating sintering desulfurization and denitrification wastewater.

[0006] MVR is the abbreviation of mechanical vapor recompression technology. MVR evaporator is an energy-saving technology that reuses the energy of the secondary steam it produces, thereby reducing the demand for external energy. The principle of the MVR evaporator is to use a high-efficiency steam compressor to compress and evaporate the secondary steam produced, increase the pressure and temperature of the secondary steam, and pump the secondary steam with increased thermal energy into the heater to heat the original liquid again. The heated original liquid continues to evaporate to produce secondary steam, thereby achieving a continuous evaporation state. Because MVR can reach a lower operating temperature, it is often used in the treatment of high-salt wastewater with complex components and volatile components. In the MVR process device for sintering desulfurization and denitrification wastewater treatment provided in the present application, an MVR evaporator is used to achieve wastewater treatment.

[0007] In the device provided herein, wastewater undergoes pretreatment to adjust its pH and remove most suspended solids before entering a single-effect forced circulation crystallization system for evaporative crystallization. This evaporative crystallization involves evaporation of the solvent and co-crystallization of calcium sulfate and a crystalline salt, ultimately yielding solid waste and reusable water. Furthermore, the process device can operate at low temperatures (<85°C), preventing scaling and equipment corrosion.

[0008] The purpose of this application can be achieved through the following technical solutions:

[0009] The present application provides an MVR process device for treating sintering desulfurization and denitrification wastewater, which is directly connected to a sintering desulfurization and denitrification wastewater pool, wherein the sintering desulfurization and denitrification wastewater pool is filled with sintering desulfurization and denitrification wastewater to be treated; the MVR process device includes a wastewater pretreatment module and an MVR low-temperature forced circulation crystallization module connected in sequence; that is, the sintering desulfurization and denitrification wastewater first enters the wastewater pretreatment module, and then enters the MVR low-temperature forced circulation crystallization module, and the wastewater treated by the system can be directly reused.

[0010] Furthermore, the wastewater pretreatment module includes a pH adjustment tank, a gravity sedimentation tank, and an intermediate water tank; the MVR low-temperature forced circulation crystallization module includes a first heat exchanger, a second heat exchanger, a flash tank, and a solid-liquid separator. The first heat exchanger is an "inlet water / condensate" heat exchanger, whose first heat exchange channel carries circulating liquid / high-salt wastewater, and whose second heat exchange channel carries condensate / recycled water; the second heat exchanger is a shell and tube heat exchanger, whose first heat exchange channel is a tube side, carrying circulating liquid / high-salt wastewater, and whose second heat exchange channel is a shell side, carrying steam / condensate / recycled water. The first heat exchanger is used for heat exchange between wastewater and condensate, and the second heat exchanger is used for heat exchange between steam and wastewater; the solid-liquid separator can realize the separation of solid waste in the device.

[0011] Furthermore, the water inlet of the pH adjustment tank is connected to the water outlet of the sintering desulfurization and denitrification wastewater tank through a pipeline, the water outlet of the pH adjustment tank is connected to the gravity sedimentation tank and the intermediate water tank in sequence through a pipeline, and the water outlet of the intermediate water tank is connected to the liquid inlet of the flash tank after passing through the first heat exchange channel of the first heat exchanger and the first heat exchange channel of the second heat exchanger in sequence through a pipeline.

[0012] Furthermore, the flash tank is also provided with a supplementary steam inlet, a steam outlet, and a circulating liquid outlet. The steam inlet of the flash tank is connected to the supplementary steam tank, and the steam outlet of the flash tank is connected to the produced water reuse pool after passing through the second heat exchange channel of the second heat exchanger and the second heat exchange channel of the first heat exchanger in sequence. The liquid outlet of the flash tank is connected to the solid-liquid separator through a pipeline. The solid-liquid separator is used to achieve solid-liquid separation. Its liquid outlet enters the first heat exchange channel of the second heat exchanger, and its solid outlet is connected to the crystallized salt dehydration pool.

[0013] Furthermore, a water inlet pump is provided on the pipeline between the pH adjustment tank and the sintering desulfurization and denitrification wastewater tank; a first suction pump is provided on the pipeline between the gravity sedimentation tank and the intermediate water tank, and a second suction pump is provided on the pipeline between the intermediate water tank and the first heat exchange channel of the first heat exchanger; a condensate drainage pump is provided between the second heat exchange channel of the second heat exchanger and the second heat exchange channel of the first heat exchanger.

[0014] Furthermore, the vapor outlet of the flash tank is connected to a mechanical vapor compressor and the second heat exchange channel of the second heat exchanger via a vapor-liquid separation device. The liquid outlet of the flash tank is connected to the solid-liquid separator via a slurry reflux pump, which also has a liquid outlet connected to the first heat exchange channel of the second heat exchanger. The solids outlet of the gravity settling tank is connected to the sludge dewatering tank, and the solids outlet of the solid-liquid separator is connected to the crystallized salt dewatering tank. The sludge dewatering tank and the crystallized salt dewatering tank are connected to the solids treatment / disposal tank; the second heat exchange channel of the first heat exchanger is connected to the produced water reuse tank, which is used for water discharge.

[0015] Furthermore, the pH adjustment tank is used to add pH adjustment reagents and equalize water quality, and the gravity sedimentation tank is used for sedimentation and neutralization reaction to form solid suspended matter.

[0016] Furthermore, a flow meter is provided on the pipeline between the pH adjustment tank and the sintering desulfurization and denitrification wastewater tank for monitoring the water inlet flow; the pH adjustment tank is provided with a pH automatic detection and analysis instrument and a pH reagent addition instrument for monitoring and adjusting the pH, the pH automatic detection and analysis instrument is used to monitor the pH value in the pH adjustment tank and the gravity sedimentation tank in real time, and the pH reagent addition instrument automatically analyzes and adds pH adjustment reagent according to the pH value monitored by the pH automatic detection and analysis instrument; the gravity sedimentation tank is provided with a stirrer for stirring and mixing the wastewater in the gravity sedimentation tank.

[0017] Furthermore, the flash tank is also provided with a plurality of sight glasses, which are made of safety glass with high transparency, good pressure resistance and corrosion resistance, and can facilitate manual inspection of the equipment operation status; the evaporator in the flash tank is made of corrosion-resistant material.

[0018] Compared with the prior art, the device provided by this application has the following advantages:

[0019] (1) This process device can fully utilize existing equipment, simplify pretreatment requirements, and reduce pretreatment operating costs. By combining the wastewater treatment device with the one-step crystallization equipment, the wastewater only needs to undergo preliminary pH adjustment and gravity precipitation before it can be directly fed into the evaporation system without the need for additional pretreatment, thus saving a large amount of pH adjustment reagents and other pretreatment reagents. The application cost is relatively low. In addition, the operation and maintenance of this device are relatively simple, reducing operating costs.

[0020] (2) The process flow of the device of the present application is very short during operation, including only wastewater pretreatment and one-step crystallization, without various intermediate water tanks, etc., and the occupied area is very small.

[0021] (3) This application uses MVR equipment, which produces water of good quality. Generally, the total dissolved solids (TDS) is below 50 mg / L and can be directly reused.

[0022] (5) The MVR low-temperature forced circulation crystallization module of the device of the present application is provided with a first heat exchanger, a second heat exchanger, a flash tank, and a solid-liquid separator. The combination of them can perform forced circulation evaporation crystallization, ensuring that there are always a large number of calcium sulfate seeds in the circulating liquid, thereby effectively controlling calcium sulfate scaling and ensuring the normal operation of the system.

[0023] (6) The present application adopts a mechanical steam compressor, which can fully utilize the heat of the secondary steam and reduce the energy consumption of the system; at the same time, there is basically no need to add chemical agents. Since the chemical cleaning cycle is long, the chemical cleaning agents can basically be ignored.

[0024] (7) This process device has a short flow, so it is very simple to operate. The technology is mature, the operation is stable and reliable, the operation mode is flexible, and the operating cost is reasonable. According to previous engineering experience, the chemical cleaning cycle can reach more than 12 months. Even after scaling, chemical cleaning will not affect the performance of the equipment (compared to reverse osmosis membranes, each chemical cleaning will reduce the equipment life).

[0025] (8) The process device of this application has a long service life and does not require replacement of core components. The core components are made of corrosion-resistant materials to ensure the service life of the entire system. The service life of the main equipment (excluding wearing parts) can reach 20 years. Unlike ultrafiltration and reverse osmosis, there is no need to replace core components every few years. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram of the MVR process module of this application;

[0027] Figure 2 This is the process flow chart of this application;

[0028] The marks in the figure indicate:

[0029] 1-first heat exchanger, 2-second heat exchanger, 3-flash tank, 4-solid-liquid separator, 5-mechanical steam compressor, 6-pump, 61-condensate drainage pump, 62-slurry reflux pump, 63-mother liquor reflux pump, 64-water inlet pump, 65-first suction pump, 66-second suction pump, 7-pH adjustment tank, 8-gravity sedimentation tank, 81-main part of gravity sedimentation tank, 82-mixer, 9-intermediate water tank, 10-vapor-liquid separation device; 11-flow meter, 12-pH automatic detection and analysis instrument; 13-pH reagent addition instrument;

[0030] A-sintering desulfurization and denitrification wastewater pool, B-steam addition device, C-product water reuse pool, D-sludge dehydration pool, E-crystallized salt dehydration pool, F-solids treatment / disposal pool;

[0031] I-wastewater pretreatment module, II-MVR low-temperature forced circulation crystallization system module. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present application, the present application is described in detail below with reference to specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application. These all fall within the scope of protection of the present application.

[0033] All raw materials in this application are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art. In the following examples, the pH, conductivity, and Cl ion concentration test standards are all referenced to national standards.

[0034] Example 1: An MVR process device for treating sintering desulfurization and denitrification wastewater

[0035] Example 1 of the present application first constructs an MVR process device for treating sintering desulfurization and denitrification wastewater, referring to Figure 1 and Figure 2 The process device includes a wastewater pretreatment system I and an MVR low-temperature forced circulation crystallization system module II.

[0036] Wastewater pretreatment system I includes a pH adjustment tank 7, a gravity settling tank 8, and an intermediate water tank 9, wherein the gravity settling tank includes a main body 81 and a mixer 82; it also includes an inlet pump 64, a first suction pump 65, and a second suction pump 66; a flow meter 11 is provided behind the inlet pump 64, and the pH adjustment tank is equipped with an automatic pH detection and analysis instrument 12 and a pH reagent addition instrument 13. MVR low-temperature forced circulation crystallization system module II includes a first heat exchanger 1, a second heat exchanger 2, a flash tank 3, a solid-liquid separator 4, a mechanical steam compressor 5, a vapor-liquid separator 10, a condensate drainage pump 61, a slurry reflux pump 62, and a mother liquor reflux pump 63;

[0037] The connection relationship of the device includes:

[0038] The water inlet of the pH regulating tank 7 is connected to the water outlet of the sintering desulfurization and denitrification wastewater pool A through a pipeline. The water outlet of the pH regulating tank 7 is connected to the gravity settling tank 8 and the intermediate water pool 9 in sequence through a pipeline. The water outlet of the intermediate water pool 9 is connected to the liquid inlet of the flash tank 3 after passing through the first heat exchange channel of the first heat exchanger 1 and the first heat exchange channel of the second heat exchanger 2 in sequence through a pipeline.

[0039] The flash tank 3 is further provided with a supplementary steam inlet, a steam outlet, and a circulating liquid outlet. The steam inlet of the flash tank 3 is connected to the supplementary steam tank B, and the steam outlet of the flash tank 3 is connected to the produced water reuse tank C after passing through the second heat exchange channel of the second heat exchanger 2 and the second heat exchange channel of the first heat exchanger 1 in sequence. The liquid outlet of the flash tank 3 is connected to the solid-liquid separator 4 through a pipeline. The solid-liquid separator 4 is used to achieve solid-liquid separation. Its liquid outlet enters the first heat exchange channel of the second heat exchanger 2, and its solid outlet is connected to the crystallized salt dehydration tank E.

[0040] A water inlet pump 64 is provided on the pipeline between the pH adjustment tank 7 and the sintering desulfurization and denitrification wastewater tank A; a first suction pump 65 is provided on the pipeline between the gravity settling tank 8 and the intermediate water tank 9; a second suction pump 66 is provided on the pipeline between the intermediate water tank 9 and the first heat exchange channel of the first heat exchanger 1; a condensate drainage pump 61 is provided between the second heat exchange channel of the second heat exchanger 2 and the second heat exchange channel of the first heat exchanger 1;

[0041] The steam outlet of the flash tank 3 is connected to the mechanical steam compressor 5 and the second heat exchange channel of the second heat exchanger 2 through the vapor-liquid separation device 10; the liquid outlet of the flash tank 3 is connected to the solid-liquid separator 4 through the slurry reflux pump 62, and the slurry reflux pump 62 also has a liquid outlet connected to the first heat exchange channel of the second heat exchanger 2;

[0042] The solid outlet of the gravity sedimentation tank 8 is connected to the sludge dewatering tank D, the solid outlet of the solid-liquid separator 4 is connected to the crystallized salt dewatering tank E, and the sludge dewatering tank D and the crystallized salt dewatering tank E are connected to the solid treatment / disposal tank F; the second heat exchange channel of the first heat exchanger 1 is connected to the produced water reuse tank C, and the produced water reuse tank C is used for water discharge.

[0043] A flow meter 11 is provided on the pipeline between the pH adjustment tank 7 and the sintering desulfurization and denitrification wastewater tank A for monitoring the water inlet flow. The pH adjustment tank 7 is provided with a pH automatic detection and analysis instrument 12 and a pH reagent addition instrument 13 for monitoring and adjusting the pH. The gravity sedimentation tank 8 is provided with a stirrer 82. The flash tank 3 is provided with a plurality of sight glasses, which are made of safety glass with high transparency, good pressure resistance and corrosion resistance, and can facilitate manual inspection of the equipment operation status; the evaporator in the flash tank is made of corrosion-resistant material.

[0044] Example 2 Process flow of an MVR process device for treating sintering desulfurization and denitrification wastewater

[0045] The wastewater from a steel desulfurization and denitrification plant was treated using the device provided in Example 1 of the present application. The process flow of the treatment was as follows:

[0046] (1) Pretreatment: The wastewater from sintering desulfurization and denitrification wastewater A is passed into the pretreatment module, the pH is adjusted, and the mixture is allowed to settle after mixing and reaction to remove suspended solids generated by heavy metal reactions in the pre-process, thereby obtaining high-salt wastewater;

[0047] (2) MVR low-temperature forced circulation crystallization system treatment: The high-salt wastewater obtained after pretreatment is passed into the MVR low-temperature forced circulation crystallization module for treatment. Through a one-step crystallization method, reusable water and solid waste are finally obtained.

[0048] In step (1), the inlet flow rate of the sintering desulfurization and denitrification wastewater is 20 to 50 m 3 / d; the sintering desulfurization and denitrification wastewater contains a large amount of salt substances and suspended matter, among which important indicators include chloride ions, sulfate ions, calcium ions, and ammonia nitrogen; the pH of the sintering desulfurization and denitrification wastewater is very low, at 1 to 2; the COD value is 500 mg / L to 1000 mg / L, and the TDS value is 50,000 mg / L to 100,000 mg / L.

[0049] In step (1), 1 to 3 mol / L sodium hydroxide is used to adjust the pH to 6 to 9 and then gravity sedimentation is started. The pH adjustment to 6 to 9 can, on the one hand, prevent the subsequent evaporation system from corroding the evaporation equipment under acidic conditions; on the other hand, it can prevent calcium carbonate scaling and ammonia nitrogen volatilization, so it is a relatively reasonable pretreatment method. In order to save alkaline reagents, after adding dilute alkali to adjust the pH, gravity sedimentation is used to remove suspended matter. Step (1) can utilize the original pretreatment system (i.e., the existing pH adjustment, sedimentation, intermediate water tank, etc.) without the need for a new pretreatment system. Most of the suspended matter is removed by adding alkali to adjust the pH to 6 to 9 and gravity sedimentation. The sludge generated in the gravity sedimentation tank is dehydrated through the original pretreatment system and treated as solid waste after dehydration.

[0050] In step (2), the high-salt wastewater obtained after the pretreatment is lifted by a suction pump connected to the intermediate water tank and directly enters the MVR low-temperature forced circulation crystallization module. The MVR low-temperature forced circulation crystallization module includes two circulation systems: low-temperature forced crystallization circulation ( Figure 2 medium orange-yellow lines) and steam condensate circulation ( Figure 2 The two are carried out simultaneously and heat exchange is achieved; in the MVR low-temperature forced circulation crystallization system, the circulating pretreated high-salt wastewater is lifted by a suction pump and first passes into the "water / condensate" heat exchanger (the first heat exchanger). After being heated by the temperature of the condensate, it is transported to the heater box of the shell and tube heat exchanger (the second heat exchanger). In the shell and tube heat exchanger, the circulating liquid is diverted to each heat exchange tube, and the flow rate is controlled at 1.5m / s to 3.0m / s to prevent crystallization or scaling from adhering to the surface of the heat exchanger and affecting the heat exchange efficiency.

[0051] High-salt wastewater (circulating liquid) flows at high speed in the heat exchange tubes of the shell and tube heat exchanger, absorbing the heat generated by the condensation of steam outside the heat exchange tubes to heat and increase the temperature. By controlling the pressure in the tubes to be lower than the saturated steam pressure at that temperature, the high-salt wastewater will not boil in the tubes. After the high-salt wastewater is heated by the shell and tube heat exchanger, it flows out and enters the separation chamber of the flash tank. Due to the sudden drop in pressure in the separation chamber of the flash tank, the high-temperature high-salt wastewater flashes here, the brine is concentrated, and crystals are precipitated. In addition, the crystals are co-crystals of calcium sulfate and crystalline salts. The secondary steam generated in the flash tank passes through the vapor-liquid separation device to remove salt droplets, and is then extracted by a mechanical steam compressor to increase the temperature and pressure. The heated steam is used as the evaporation heat source of the heat exchanger in the shell side of the shell and tube heat exchanger to achieve cyclic mechanical heating and evaporation. The distilled water condensed in the heat exchanger is discharged after heat exchange. The high-salt wastewater crystals produced in the flash tank are further concentrated and crystallized as part of the fluid passes through the slurry reflux pump. The concentrated liquid part flows back into the shell and tube heat exchanger, and the crystal part is separated by the solid-liquid separator. The separated liquid also flows back into the shell and tube heat exchanger, and the solid crystals are treated / disposed of as solid waste.

[0052] In the MVR low-temperature forced circulation crystallization module, the pressure in the flash tank is maintained at 500-600 Pa and the temperature is maintained at 50-60° C.; the temperature of the rest of the system is maintained below 85° C.

[0053] The one-step crystallization method described in step (2) refers to the process of continuously increasing the salt concentration (i.e., saturation) in the circulating liquid by mechanical compression and continuous evaporation of the solvent, so that it reaches a supersaturated state, causing the solution concentration to exceed the theoretical equilibrium concentration, thereby generating a new phase; there are a large number of calcium sulfate seed crystals in the flash tank, so that most of the crystallization in the treatment system can be controlled to occur in the flash tank rather than in the pipeline, further avoiding pipeline scaling.

[0054] In order to control calcium sulfate scaling and reduce system corrosion, the present application controls the system to operate at a low temperature below 85°C through a slurry reflux pump. Under low temperature conditions, the newly crystallized calcium sulfate is calcium sulfate dihydrate (gypsum), and gypsum is a soft crystal that will not cause scaling of the heat exchange tubes. In addition, the pretreated wastewater evaporation process adopts a one-step crystallization method, that is, the wastewater is directly fed into the crystallizer without concentration. In the one-step crystallization process, crystallized salt and calcium sulfate are precipitated together in the crystallizer, making it easier to control scaling. The circulating fluid contains a large amount of calcium sulfate and crystallized salt crystals, which will cause a great scouring of the heat exchange tubes, thereby controlling calcium sulfate scaling. At the same time, the scale is a mixed scale of calcium sulfate and crystallized salt, and the crystallized salt can be dissolved by hot water to perform descaling.

[0055] Furthermore, for the evaporation system in the flash tank, the main factors affecting system operation are scaling control and product water quality assurance measures. The evaporator of this evaporation system adopts a forced circulation evaporation low-temperature mode operated under slightly acidic conditions and with seed crystal addition to avoid equipment scaling. The technical solution of this application prevents scaling and ensures product water quality through the following methods / principles:

[0056] 1) Operation under slightly acidic conditions: Under slightly acidic conditions with a pH of 5, carbonate and bicarbonate in the wastewater will basically not form calcium carbonate scaling, so calcium carbonate scaling can be effectively controlled;

[0057] 2) Forced circulation crystallizer: The forced circulation evaporation crystallizer adopts external heating. The wastewater is heated in the heat exchanger and flash evaporated in the separation chamber of the flash tank. The concentration of the wastewater does not change during the heating process, but the concentration increases after flash evaporation in the separation chamber. Therefore, crystals such as calcium sulfate will precipitate in the separation chamber of the flash tank, avoiding the precipitation of crystals on the wall of the heat exchange tube and causing scaling of the heat exchange tube;

[0058] 3) Surface attachment and growth of calcium sulfate seed crystals: There is always a certain concentration of calcium sulfate seed crystals in the separation chamber of the flash tank. The precipitated calcium sulfate crystals will preferentially grow on the surface of the seed crystals rather than on the wall of the heat exchange tube, further avoiding the possibility of scaling on the wall of the heat exchange tube;

[0059] 4) Flushing effect of crystals: A large-flow mother liquor reflux pump is used for forced circulation, so that the circulating liquid runs at high speed in the heat exchange tubes. The flow rate is controlled at 1.5m / s to 3.0m / s. The high flow rate of the circulating liquid through the heat exchange tubes reduces the occurrence of scaling. At the same time, the circulating liquid contains a large amount of calcium sulfate and crystallized salt crystals, which will cause a great flushing of the heat exchange tubes, thereby controlling calcium sulfate scaling.

[0060] 5) Low temperature conditions: When operating at a low temperature of 85°C, the newly crystallized calcium sulfate is gypsum (calcium sulfate dihydrate). Gypsum is a soft scale and is not likely to cause scaling of the heat exchange tubes.

[0061] 6) Co-crystallization: This process adopts a one-step crystallization process. Calcium sulfate, calcium sulfate and crystalline salt are crystallized and precipitated at the same time. Therefore, even if scale is formed, it is a mixed scale of calcium sulfate and crystalline salt. Therefore, as long as hot water is passed to melt the crystalline salt, the calcium sulfate scale can be easily cleaned off, saving a lot of calcium sulfate cleaning chemical costs.

[0062] Example 3 Actual treatment effect of the MVR process device for sintering desulfurization and denitrification wastewater treatment

[0063] This example uses the device provided in Example 1 and the process flow provided in Example 2 to treat wastewater from a steel desulfurization and denitrification plant (see Table 1). The water flow rate in the system is 50m 3 / d.

[0064] The influent indicators are: COD 500-1000 mg / L, TDS 50000-100000 mg / L, pH 1-2, conductivity >20000μs / cm, Cl concentration 26996 mg / L, ammonia nitrogen concentration 34.5 mg / L, total nitrogen concentration 85.0 mg / L, and total phosphorus concentration 0.45 mg / L.

[0065] The effluent indicators are: pH value 6-9, conductivity ≤100μs / cm, Cl concentration ≤50mg / L, TDS ≤50mg / L, and the remaining COD, ammonia nitrogen, total nitrogen and total phosphorus are undetectable.

[0066] Table 1 Wastewater treatment effect in Example 3 of this application

[0067]

[0068] Electrical conductivity measures the electrical conductivity of water. The conductivity of water is related to the amount and type of dissolved electrolytes. Conductivity reflects the total dissolved solids content in the water, including organic matter and inorganic salts. High conductivity may indicate contamination or other environmental issues.

[0069] After being treated with this device, the conductivity and Cl concentration of the wastewater were reduced by more than 99.5%, and the nitrogen and phosphorus concentrations were reduced to undetectable levels, indicating that the wastewater treatment effect was good and the wastewater can be used as recycled water in industry.

[0070] The “-” in the table means that the substance can no longer be detected in the water.

[0071] Example 4 Actual treatment effect of the MVR process device for sintering desulfurization and denitrification wastewater treatment

[0072] This example uses the device provided in Example 1 and the process flow provided in Example 2 to treat wastewater from a steel desulfurization and denitrification plant (see Table 2). The water flow rate in the system is 20m 3 / d.

[0073] The influent indicators are: COD 800-1000 mg / L, TDS 80,000-100,000 mg / L, pH 1-2, conductivity >20,000 μs / cm, Cl concentration 30,000 mg / L, ammonia nitrogen concentration 50 mg / L, total nitrogen concentration 90 mg / L, and total phosphorus concentration 1 mg / L.

[0074] The effluent indicators are: pH value 6-9, conductivity ≤100μs / cm, Cl concentration ≤50mg / L TDS ≤50mg / L, and the remaining COD, ammonia nitrogen, total nitrogen and total phosphorus are undetectable.

[0075] Table 2 Wastewater treatment effect in Example 4 of this application

[0076]

[0077] The “-” in the table means that the substance can no longer be detected in the water.

[0078] After being treated with this device, the conductivity and Cl concentration of the wastewater were reduced by more than 99.5%, and the nitrogen and phosphorus concentrations were reduced to undetectable levels, indicating that the wastewater treatment effect was good and the wastewater can be used as recycled water in industry.

[0079] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, this application is not limited to the above-described embodiments. Any improvements and modifications made by those skilled in the art based on the disclosure of this application, without departing from the scope of this application, should be within the scope of protection of this application.

Claims

1. An MVR process device for treating sintering desulfurization and denitrification wastewater, the device being directly connected to a sintering desulfurization and denitrification wastewater pool (A), wherein the sintering desulfurization and denitrification wastewater pool (A) is filled with sintering desulfurization and denitrification wastewater to be treated; It is characterized by: The MVR process device includes a wastewater pretreatment module (I) and an MVR low-temperature forced circulation crystallization module (II); The wastewater pretreatment module (I) includes a pH adjustment tank (7), a gravity sedimentation tank (8) and an intermediate water tank (9); the MVR low-temperature forced circulation crystallization module (II) includes a first heat exchanger (1), a second heat exchanger (2), a flash tank (3), and a solid-liquid separator (4). The water inlet of the pH regulating tank (7) is connected to the water outlet of the sintering desulfurization and denitrification wastewater tank (A) through a pipeline, and the water outlet of the pH regulating tank (7) is connected to the gravity sedimentation tank (8) and the intermediate water tank (9) in sequence through a pipeline, and the water outlet of the intermediate water tank (9) is connected to the liquid inlet of the flash tank (3) after passing through the first heat exchange channel of the first heat exchanger (1) and the first heat exchange channel of the second heat exchanger (2) in sequence through a pipeline; The flash tank (3) is further provided with a supplementary steam inlet, a steam outlet, and a circulating liquid outlet. The steam inlet of the flash tank (3) is connected to the supplementary steam tank (B), and the steam outlet of the flash tank (3) is connected to the produced water reuse pool (C) after passing through the second heat exchange channel of the second heat exchanger (2) and the second heat exchange channel of the first heat exchanger (1) in sequence. The liquid outlet of the flash tank (3) is connected to the solid-liquid separator (4) through a pipeline. The solid-liquid separator (4) is used to achieve solid-liquid separation. Its liquid outlet enters the first heat exchange channel of the second heat exchanger (2), and its solid outlet is connected to the crystallized salt dehydration pool (E).

2. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: A water inlet pump (64) is provided on the pipeline between the pH regulating tank (7) and the sintering desulfurization and denitrification wastewater tank (A); a first suction pump (65) is provided on the pipeline between the gravity sedimentation tank (8) and the intermediate water tank (9); and a second suction pump (66) is provided on the pipeline between the intermediate water tank (9) and the first heat exchange channel of the first heat exchanger (1).

3. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: A condensate drainage pump (61) is provided between the second heat exchange channel of the second heat exchanger (2) and the second heat exchange channel of the first heat exchanger (1).

4. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: The steam outlet of the flash tank (3) is connected to the mechanical steam compressor (5) and the second heat exchange channel of the second heat exchanger (2) through the vapor-liquid separation device (10).

5. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: The liquid outlet of the flash tank (3) is connected to the solid-liquid separator (4) via a slurry reflux pump (62), and the slurry reflux pump (62) also has a liquid outlet connected to the first heat exchange channel of the second heat exchanger (2).

6. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: The solid outlet of the gravity sedimentation tank (8) is connected to the sludge dewatering tank (D), the solid outlet of the solid-liquid separator (4) is connected to the crystallized salt dewatering tank (E), and the sludge dewatering tank (D) and the crystallized salt dewatering tank (E) are connected to the solid treatment / disposal tank (F); the second heat exchange channel of the first heat exchanger (1) is connected to the produced water reuse tank (C), and the produced water reuse tank (C) is used for water discharge.

7. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: A flow meter (11) is provided on the pipeline between the pH regulating tank (7) and the sintering desulfurization and denitrification wastewater tank (A) for monitoring the water inlet flow.

8. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: The pH regulating tank (7) is provided with a pH automatic detection and analysis instrument (12) and a pH reagent adding instrument (13) for monitoring and regulating pH.

9. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: A mixer (82) is provided in the gravity sedimentation tank (8).

10. The MVR process device for treating sintering desulfurization and denitrification wastewater according to claim 1, characterized in that: A plurality of sight glasses are provided in the flash tank (3).

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